The present invention relates to a machine for treating sheets, in particular for manufacturing packaging made of materials such as cardboard or plastic, said machine comprising drive means having at least one drive motor and suitable for driving sheets in a drive direction through a treatment zone situated between the inlet and the outlet of the machine, treatment tooling designed to form cutouts and/or folds that are disposed transversely relative to the drive direction in said sheets, means for determining information relating to the position of a sheet in the treatment zone, and control means for controlling the treatment tooling as a function of said information.
For manufacturing packaging from sheets of cardboard or of plastic, firstly xe2x80x9ctransversexe2x80x9d machines of the above-mentioned type are known in which at least the majority of the cutouts or folds are provided transversely relative to the advance direction in which the sheets advance through the machine. Secondly, xe2x80x9clongitudinalxe2x80x9d machines are known, e.g. of the type described in the Applicant""s Patent Application EP 0 539 254, in which the majority of the folds and of the cutouts are provided in the advance direction in which the sheets advance through the machine.
Longitudinal machines reach high manufacturing throughputs. The various manufacturing steps are performed by cylinders turning at high speeds. The developed length of each cylinder determines the length of the sheets that it is possible to treat in the machine. As a result, with any given longitudinal machine, it is possible to manufacture only items of packaging whose length varies within a narrow range determined by the minimum and maximum developed lengths of the machine.
In transverse machines of known type, the various tools (cutting tools, scoring tools) are carried by beams which are disposed transversely relative to the advance direction in which the sheets advance, and which can be moved vertically between working positions and retracted positions. Various tools can be mounted on the beams, which makes it possible to manufacture a variety of items of packaging. However, the sheet treatment operations performed by the cutting or scoring tools can be performed only while the sheets are stationary. Thus, the drive means advance the sheets stepwise between each treatment step. As a result, the manufacturing throughputs of known transverse machines are very low since, for example, they reach only 300 boxes per hour.
The invention proposes to improve transverse machines of the type mentioned in the introduction so as to enable them to reach manufacturing throughputs that are significantly higher, e.g. of the order of 1000 boxes per hour.
This object is achieved by means of the facts that the treatment tooling is carried by at least one transverse carrier shaft rotated by a shaft motor which is distinct from said at least one drive motor, that the drive means are suitable for driving the sheets at a substantially constant drive speed between the inlet and the outlet of the machine, and that said machine further comprises a control unit suitable for acting as a function of said advance speed and of the information relating to the position of a sheet in the treatment zone, to control the shaft motor such that, for treating said sheet, the tooling is in contact with a predetermined region of the sheet and is driven at a treatment speed whose tangential component is equal to said drive speed.
Unlike the prior art for transverse machines, which drive the sheets through the machine stepwise, the invention thus proposes to drive the sheets at substantially constant speed, without any stop stage. The tooling serving to form the transverse folds or cutouts is carried by the carrier shaft which is disposed transversely relative to the drive direction in which the sheets are driven, and which is driven by a shaft motor that is specific to it. Since it knows the drive speed at which the sheets are driven, the position of the tooling on the transverse carrier shaft, the position of a sheet in the treatment zone, and the positions of the cutouts or folds that are to be formed in said sheet, the control unit of the machine controls the shaft motor of the carrier shaft, rather than the sheet drive means, so that, during sheet treatment, the tooling is accurately in contact with that region of the sheet in which a fold or cutout is to be formed, and is driven at a treatment speed equal to the drive speed.
In other words, instead of servo-controlling the drive of the sheets on predetermined positions of the treatment tools, the invention makes provision to use an electronic control unit to servo-control the positions and the speeds of the treatment tools on the sheet and on the speed at which said sheet is driven.
The shaft motor must be sufficiently reactive and flexible for its speed to increase and decrease within a very short lapse of time so as to be controlled to operate at a precise value which is the drive speed at which the sheets are driven. For example, a positioning motor such as a motor having a multi-pole shaft that delivers torque that is substantially constant both at low speed and at high speed can be suitable. It is also possible to choose an electric motor of the asynchronous type or a brush-less motor.
In known transverse machines, it is possible to fit various tools to the same beam by aligning them transversely. In which case, cutouts or folds to be formed in two regions of the sheet that are spaced apart in the advance direction in which the sheet advances must be formed either by the same beam during two successive stops of the sheet passing under said beam, or by two spaced-apart beams.
Also to achieve the object of increasing manufacturing throughputs, the invention advantageously makes it possible, to perform two treatments (cutting or folding) on the sheet in two zones spaced apart from each other in the drive direction in which said sheet is driven, and to do so using the same carrier shaft.
Thus, advantageously, the machine has a carrier shaft with angular tool adjustment comprising a hub, a fixed tool holder secured to the hub, and a moving tool holder secured to a moving support which co-operates with the hub via position adjustment means making it possible to adjust the angular position of the moving tool holder relative to the fixed tool holder.
In which case, it is possible not only to treat two spaced-apart zones of the sheet by means of tools carried by respective ones of the two tool holders, but also to adapt the machine rapidly to accommodate different types of packaging, for which the spacing between said zones is different, by moving the moving tool holder relative to the fixed tool holder.
In which case, advantageously, the fixed tool holder is fixed to the hub by being disposed on a first cylinder generator line, the moving support comprises at least one band to which the moving tool holder is fixed along a second cylinder generator line, said band being coaxial with the hub, having an inner set of teeth and extending, in the region of the first generator line in a space provided between the outside surface of the fixed tool holder and the hub, and the position adjustment means comprise a cog shaft which is disposed between the hub and the band while co-operating with the inner set of teeth of said band, and means for driving the cog shaft in rotation, so as to cause the band to turn relative to the hub and thus to adjust the angular positioning of the second generator line relative to the first generator line.
This simple and reliable configuration makes it very fast to modify the angular spacing between the moving tool holder and the fixed tool holder, to adapt the machine to manufacturing different items of packaging.
Advantageously, the carrier shaft has at least one tool holder equipped with fast fixing means for a tool, which means comprise a longitudinal fixing groove situated on the outside surface of the tool holder, at least one of the longitudinal edges of said groove being a moving edge and being defined by a wedging piece that is mounted to move between a locking position, in which it co-operates with the opposite edge to define a retaining profile suitable for retaining a fixing rib having a complementary profile, and an unlocking position, in which the edge is spaced apart from the opposite edge to enable the fixing rib to be inserted into said groove, by moving the rib radially towards the axis of the carrier shaft.
To achieve the general object of avoiding any unnecessary loss of time while the machine is being used, the invention thus makes it possible to simplify fitting the tools to the carrier shaft by using the fast fixing means.
Advantageously, the machine has a multiple tool carrier shaft suitable for carrying at least first and second tools spaced angularly apart, and the control unit is suitable for controlling the shaft motor of said multiple tool carrier shaft in compliance with a cycle comprising a first tool treatment stage during which the first tool is in contact with a first determined region of a sheet situated in the treatment zone of the machine and is driven at a tangential velocity equal to drive speed at which said sheet is driven, a positioning phase during which the multiple tool carrier shaft is driven to position the second tool in a situation in which it can treat a second determined region of the sheet, and a second tool treatment stage, during which the second tool is in contact with said second region and is driven at a tangential velocity equal to the drive speed.
With the carrier shaft with angular tool adjustment, having a fixed tool holder and a moving tool holder, it is possible to adjust the position of the moving tool holder so that said carrier shaft turns at the same speed (which, converted to tangential velocity is equal to the drive speed at which the sheets are driven through the machine) during the first tool treatment stage, during the positioning stage, and during the second tool treatment stage. In which case, the angular spacing between the two tools corresponds to the distance between the two treatment zones in which the two tools must respectively act. In certain cases, even with the carrier shaft with angular tool adjustment, the positioning stage can nevertheless be performed at a speed somewhat different from the drive speed at which the sheets are driven.
However, the multiple tool carrier shaft may also carry different tools in determined zones and may be driven during the positioning stage at a speed that is higher or lower than the drive speed at which the sheets are driven so as to put the second tool in the proper position for the second tool treatment stage.
Advantageously, the machine has means for moving the multiple tool carrier shaft away from the advance path along which the sheets advance through the treatment zone during the positioning stage.
For example, the multiple tool carrier shaft may carry three or four tools spaced apart angularly, an intermediate tool being interposed between the first and second above-mentioned tools, e.g. to be used optionally. In which case, the multiple tool carrier shaft is driven at a speed corresponding to the drive speed at which the sheets are driven for the first tool treatment stage, is then moved away from the advance path along which the sheets advance, and, while in this situation, can be moved rapidly to position the second tool in a situation for treating the second determined region of the sheet, without the intermediate tool coming into contact therewith.
In an advantageous variant, the drive means co-operate with adjustable-position drive wheels which are mounted on wheel supports, and the machine has means for adjusting the positions of said supports transversely relative to the drive direction in which the sheets are driven through the machine.
It is desirable to dispose the drive wheels in positions determined by the width of the sheet, as measured in the transverse direction. For example, the adjustable-position drive wheels must support particular zones of the sheet or form certain cutouts or certain folds which must be disposed parallel to the drive direction in which the sheets are driven.
In which case, the machine has at least one adjustment belt disposed transversely relative to the drive direction in which the sheets are driven, means for driving said belt, and coupling means suitable for being caused to go between a coupling situation in which they secure a wheel support to said belt, and a stop position in which they secure said wheel support to a fixed locking part.
Thus, the wheel supports and therefore the wheels that they carry are easy to move relative to one another without it being necessary to remove them.